Multiple way inverse feed-back connection



Aug. 28, 1956 E. LEUTHOLD MULTIPLE NAN INVERSE FEED-BACK CONNECTION Filed Aug. 1, 1951 INVENTOR. gen Leustkol Byx YMAWSZ 96+ United States Patent MULTIPLE WAY INVERSE FEED-BACK CONNECTION Eugen Leuthold, Neuhausen, Switzerland Application August 1, 1951, Serial No. 239,714

Claims priority, application Germany August 10, 1950 3 Claims. (Cl. 179171) This invention relates to a multiple path inverse feedback connection and is especially applicable to high frequency resonant circuits as they are used in radio receivers for example. In its more general aspects, the invention mainly consists in the compensation of certain phase displacements which, when present, adversely affect the resonance curve of the resonant circuits. It is, therefore, the main object of the invention to improve the shape of the resonance curve by eliminating such phase displacements and, incidentally, to thereby improve the sound transmitting properties of the radio receiver.

In the multiple path inverse feed-back circuits which have been known up to the present it has been found, that the resonance curve of tuned high or intermediate frequency amplifier stages attains a substantial slope simultaneously with increased band width thereof. It is, consequently, the most important object of the present invention to provide an amplifier circuit having a resonance curve of substantially rectangular shape.

In order to comply with this requirement asfar as possible, very small inverse feed-back impedances have to be employed. However, these impedances have the disadvantages that asymmetries thereof will appear when capacitative or inductive, that is, non-resistive inverse feed-back impedances are used. As a consequence the resonance curve also becomes asymmetric, which causes distortions and, in extreme cases, even causes a tendency to oscillate.

In order to eliminate these difficulties and to produce a broad resonance curve having steep sides, the invention mainly consists of the compensation of adverse phase displacements or shifts of the current in relation to the generating inverse feed-back voltage by the employment of impedance elements which are connected to produce phase coincidence. The invention thus provides the necessary phase coincidence by compensating for the adverse phase displacements or shifts of the current in relation to the inverse feed-back voltage, which are introduced by the interaction of the capacitative and/or inductive impedances as well as the resistive impedances in the amplifier circuit. This phase coincidence and correction is produced by the employment of impedances such as are capable of achieving this result.

The adverse phase displacements or shifts of the occurring currents in relation to the respective inverse feedback voltage can hereby be suitably compensated by the use of a phase-reversing circuit, to be explained more fully hereinafter, which is connected in parallel and/ or in series with capacitative and/or inductive impedances.

A further feature of the invention resides in obtaining the required phase coincidence by an additional path of inverse feed-back consisting of a phase-reversing circuit applied to a point of inverse feed-back voltage of more than 90 displacement. Preferably a phase displacement of 180 will be imparted to the inverse feed-back voltage.

A further modification of the present invention consists in procuring the symmetry of the inverse feed-back resistance R2.

, 2,761,021 Patented Aug. 28, 1956 Fig. 2 shows a circuit in accordance with the invention with an additional inverse feed-back;

Fig. 3 shows a modified embodiment of the invention in which purelyresistive impedances and a phase bridge for the additional inverse feed-back are used; and

Fig. 4 is a vector diagram forexplaining the phase relationships of the voltages and currents in the feedback circuits of the present invention.

In Fig. 1 a known form of the multiple inverse feedback circuit is shown, in which an inverse feed-back is produced in the two circuits 1 and 2 by the resonant circuit 3, whereby all circuits are controlled with a single tube 4. One inverse feedaback path leads from the resonant circuit 3 through the resistance R2 to the resonant circuit 2, and another inversefeed-back path through the condenser C1 'to the resonant circuit 1.

Fig. 2 illustrates a multiple path inverse feed-back coni nection in accordance with the present invention in which an additional inverse feed-back path is introduced in the resonant circuit 1, which leads to this circuit through an inductor Li thereby causing a voltage which is in opposite phase to the feed-back voltage-caused by capacitor A further embodiment of the invention is shown in Fig. 3. In this figure, a first inverse feed-back path leads in' known manner to the resonant circuit 2 through the In addition, a second inverse feed-back path leads to the resonant circuit 1 by means of a phase bridge CY-R C R, consisting ofcapacitors C and resistoi's R, and by means of resistor R1. It is apparent that the resonant circuit 1 of Figs. 2 and 3 is a tuned circuit which appears in the output stage of the amplifier preceding the amplifier circuit incorporating the present invention.

In both embodiments of the invention as shown in Figs. 2 and 3 all the circuits are controlled by only a single tube 4.

Referring now to Fig. 4 and to Fig. 2 to which it refers, the feed-back voltage across resistor R2 in the feedback branch leading to tuned input circuit 2 is represented by vector E. For optimum performance it is desirable that the feed-back of energy to the tuned output circuit 1 of the immediately preceding stage be precisely out of phase with the energy fed back to the tuned input circuit 2. It might appear that this could be accomplished merely by using a capacitive feed-back path. However, because of the resonant resistance (R1) of tuned circuit 1, the voltage across capacitance C1 has a phase relationship relative to E as illustrated by the vector E0, and the voltage across resistor R1 is B3,. The I current through capacitance C1 leads the voltage thereacross by 90 as indicated by the dashed line vector 10,.

The voltage E across the inductive branch of the feedback path is also broken up into two components, EL1 across coupling coil L1 and ER, across the resistor R1. These vectors are indicated in Fig. 4. The current through coupling coil L1 lags the voltage thereacross by 90 and is indicated on the vector diagram by the dashed line 1L1. As the inductive branch of the feed-back path is supplied to one end of the coil inductively coupled to tuned circuit 1 and the capacative branch to the other end of this coil, current vector Ir. may be indicated by a second vector IL, which is out of phase with 11.

As can be seen from the attached vector diagram in Fig. 4, the resultant of current vectors Ic and I'L, is a currentl indicateda-by vectorl which is precisely'90 out of phase, with the. yoltage...acrossiresistor, RztandJhere;

fore the current through resistor R2.

The embodiments are shown in a diagrammatic form and as applied to;only;threecircuits; Itstands to reason:

that, without departing from the spirit of'zthexinvention they may beappliedziwith the samelresultotowa greater numbercof; circuits; o.

What I claim and :ddSiIGCiSIOnSfiCHIZB :by- Letters Patent;

of the United; States is:

1. A circuit arrangement comprising-11incombination,-

an :amplifier stagmhavinga tuneddnput circuitiand a tuned output circuitg-annadditional. tuned circuit coupled;

to said. tuned input circuit :for: feeding energy thereto; a

resistive first feed-back;path-trom said :tuned output cir-I cuit to said. tuned input circuit Eton-supplying a negative:

feedback energywtojsaid tuned input circuit; and means aifordinga secondfeed-back pathrfromvsaid tuned output circuit to said additional:tuned-"circuitwcomprising.tcoufa.

pling-means coupled-rte the tunedoutput circuit, vcapacitive means defining one path-:lportion between-said .coue:

coupling an intermediatepoint between said first andsec- 0nd path-portions to =said..'coupling :means for feeding" v energy to said additional:tuned-circuit. which leads sin back'path to said tuned-input circuit by precisely-90 2. A circuit arrangement comprising, :in' combination,

an amplifier stage 'havinga -tuned==input circuit and a.

tuned output circuit; an additional:tuned circuit coupledw tosaid tuned input circuit for feeding energy theretoyaw resistive first feed-back path from said tuned output Cit cuit to' said tuned input circuition-supplying negative feed-back energy to said tuned input circuit, comprising a coil coupled to said input circuit and a resistor coupled between said output tunedcircuit andrsaid coil;' and means,

affording a second feed-backpath from. said tuned output; circuit towsaid additional,;tuned circuit comprising coll-1 pling means coupled to the tuned output circuit, capacitive means defining one path portion between said coupling means and said additional tuned circuit, inductive means defining a second path portion between said coupling means and said additional tuned circuit and means coupling an intermediate point between said first and second path portions to said coupling means for feeding energy by said additional tuned circuit which leads in phase the energyfedpback-by means of-saidfirst feedback path to said tuned input circuit by precisely 3. A circuit arrangementcomprising, in combination, an amplifierstagehaving a tuned input circuit and a tuned output circuit; an additional tuned circuit-coupled to said; tuned :input, circuit. for feeding energy theretog a resistive first feed-back path from said tuned output circuit to said tunedinput circuit for supplying negative feed-back energy to said tuned input circuit; and means afiording a second feed-back path from said tuned outpUiI;:CiICl1ii-, to; said; additional; tuned, :circuit for feeding energyto; said. additional tuned circuitwhich leads in phase the energy; fed back to said: tuned, input. circuit by precisely 903., c0mprising,,means coupled to the tuned output circuit, a coiLhaving apair of,inpu t terminals and being \coupled-tohsaidtadditional: tunedv circuit, capacii tive impedance means coupling negative.feed-backenergy from said meansmoupled to=.the tuned output .circuit .to one of saidinput terminals, inductivew impedance means coupling negative:feed-backzrenergy .from. saidameans I coupled to thestunedoutput circuit to the other of said terminals,and=-means coupling an intermediate point on saidcoil to said means-coupled .-to..the output circuit.

References Cited inthe ,file of this patent UNI I ED STATES PATENTSH 2,155,137 Wheeler Apr; 25,1939 2,205,075" Wilhelm June 18,1940- 2,268,672- Plebanski Jan. 6, "1942" 2,333,867 K'o'ch' Aug. 28, 1945 2,404,809 OBrien July 30,1946' 2,455,471, Crane Dec. 751948 

